Casting of metals

ABSTRACT

A sliding gate valve assembly for use in the casting of metals comprises a resilient device comprising two pad members resiliently urgeable relative to each other by spring means to urge a sliding gate member of the assembly into sealing engagement with a seating therefor and in the event of failure of the spring means, relative movement of said members is severely restricted to correspondingly restrict movement of the gate member away from the seating.

1 Dec. 16, 1975 1 CASTING OF METALS [75] Inventor: Robert Duncan Hind,Rotherham,

England [73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

[22] Filed: Aug. 10, 1973 [21] Appl. No.: 387,570

[30] Foreign Application Priority Data Aug. 25, 1972 United Kingdom 1.39618/72 [52] US. Cl. 251/144; 251/155; 251/176; 251/193 [51] Int. Cl.F16K 51/00 [58] Field of Search 251/144, 155, 176, 193; 267/162 [56]References Cited UNITED STATES PATENTS 2,337,817 12/1943 Hertrich251/176 X 2,387,266 10/1945 Holland 267/162 X 2,708,110 5/1955 Clay267/162 3,480,186 11/1969 Grosko 251/175 X 3,507,486 4/1970Schwaller.... 267/162 X 3,511,471 5/1970 Rossi 251/144 PrimaryExaminerHarold W. Weakley Attorney, Agent, or Firm-Walter P. WoodABSTRACT 11 Claims, 10 Drawing Figures US. Patent Dec. 16,1975 Sheet 1of6 3,926,406

\mm QR m GE E US. Pawnt Dec. 16, 1975 Sheet20f6 3,926,406

US. Patent Dec.16,1975 Sh eet3 of6 3,926,406

294 /92 \x. f 296 g 250 A50 US. Patent Dec. 16,1975 Sheet60f6 I3,926,466

FIGIQ CASTING or METALS This invention is concerned with improvements inor relating to the casting of metals including for example steel,aluminium and brass.

In for example one process for the continuous casting of steel, the flowof molten steel from a bottom pour ladle or tundish is controlled by asliding gate valve assembly, in which a sliding gate member is arrangedto slide in contact with a stationary orifice plate. Examples of suchsliding gate valve assemblies are described in J. T. Shapland US. Pat.No. Re. 27,237 and U.S. Pat. No. 3,501,068, and in E. P. Shapland et al.application Ser. No. 377,385, all of common ownership. These patents andapplication describe arrangements in which the sliding gate member moveslinearly; in an altemative arrangement the gate is rotary, and oneexample of this is described in Lyman U.S. Pat. No. 3,430,644, likewiseof common ownership.

Advantageously the gate member is urged against the stationary orificeplate by springs to provide a yieldable seal between the sliding gatemember and orifice plate; and advantageously the gate member and orificeplate each comprise a refractory body encased in a thinwalled metalcasing to provide required mechanical and structural properties incombination with required refractory properties.

The springs are subject to considerable stresses in operation includingat times severe heat stresses. Thus, there is a risk of springrelaxation and spring failure followed by movement of the gate memberdownwardly away from the stationary orifice plate and consequent leakageof molten steel.

It is an object of the present invention to provide an improvedresilient device adapted for use in a sliding gate valve assembly in thecasting of metals.

It is another object of the invention to provide a sliding gate valveassembly comprising such a resilient device.

It is another object of the invention to provide a metal casting plantcomprising such a sliding gate valve assembly.

The invention provides a resilient device adapted for use in a slidinggate valve assembly in the casting of metals and comprising two padmembers resiliently urgeable relative to each other to urge a slidinggate member of the assembly into sealing engagement with a seatingtherefor when the device is in use; the arrangement being such that inthe event of resilient failure between the urgeable members, relativemovement of said members is severely restricted to correspondinglyrestrict movement of the gate member away from the seating when thedevice is in use.

For example movement of the gate member away from the seating may berestricted to between five and thirty thousandths of an inch eg abouttwenty thousandths of an inch, as compared with prior art.

The invention also provides a self-contained resilient device adaptedfor use in a sliding gate valve assembly in the casting of metals andcomprising (a) a core member, (b) opposed pad members mounted on thecore member for relative movement of the pad members in directionslongitudinal of the core member, and (c) spring means acting between thepad members to urge the pad members relative to each other, said springmeans comprising a disc spring mounted around the core member.

The invention also provides a resilient device adapted for use in asliding gate valve assembly in the casting of metals and comprising twopad members and spring means between the pad members, the pad membersbeing resiliently urgeable apart by the spring means to urge a slidinggate member of the assembly into sealing engagement with a seatingtherefor when the device is in use, and the spring means comprising afirst spring assembly which when the device is in use is normallyresiliently operative to urge the pad members apart, and a second springassembly which is relaxed when the first spring assembly is resilientlyoperative and becomes resiliently operative to urge the pad membersapart in the event that the first spring assembly becomes inoperative.

The invention also provides a sliding gate valve assembly comprising asliding gate member, a seating for said sliding gate member, and aself-contained resilient device adapted to urge the sliding gate memberinto sealing engagement with the seating, said device comprising springmeans which comprises a disc spring.

The invention also provides a sliding gate valve assembly comprising asliding gate member, a seating for said sliding gate member, and aresilient device comprising: (a) two pad members resiliently urgeablerela tive to each other to urge the sliding gate member into sealingengagement with the seating, one pad member being adjacent the slidinggate member, and the other remote therefrom, (b) a core member on whichthe pad members are mounted for relative movement of the pad members indirections longitudinal of the core member, the pad member which isadjacent the sliding gate member being fixed to the core member, and (0)spring means around the core member acting between the pad members tourge the pad members apart, the core member extending in a directionaway from the sliding gate member towards stop means for severelyrestricting its movement in the event of failure of the spring means,whereby movement of the gate member away from the seating iscorrespondingly restricted.

The invention also comprehends in combination or as a kit of parts aresilient device according to the invention and a refractory bodyencased in a thin-walled metal casing, which may be provided by asliding gate member or a stationary orifice plate.

The thin-walled metal casing is for example of steel having a wallthickness between 2.5 and 3.5 mm. eg I about 3.0 mm.

It will be realised that either one or both of the sliding gate memberand stationary orifice plate comprises a refractory body encased in athin-walled metal casing.

The invention also comprehends method aspects.

There now follows a description, to be read with reference to theaccompanying drawings, of a sliding gate valve assembly embodying theinvention. This description, which is also illustrative of methodaspects of the invention, is given by way of example of the inventiononly and not by way of limitation thereof.

In the accompanying drawings:

FIG. 1 shows a sectional side view of the sliding gate valve assemblyembodying the invention;

FIG. 2 shows an enlarged sectional side view of a resilient device ofthe assembly;

FIG. 3 shows a first modified resilient device;

FIG. 4 shows a second modified resilient device;

FIG. 5 shows a third modified resilient device;

FIG. 6 shows a sectional view of a conical disc spring;

FIG. 7 shows a fourth modified resilient device;

3 FIG. 8 shows a section on the line VIIIVIII of FIG.

FIG. 9 shows a section on the line IXIX of FIG. 1; and

FIG. 10 shows an exploded perspective view of certain parts also shownin FIG. I with a toggle mechanism thereof in a released condition and asliding gate carrier shown in a hingedly released vertical position.

The sliding gate valve assembly (FIGS. 1, 8, 9 and 10) embodying theinvention is adapted for use in the casting of steel into an ingot mould(not shown) or a tundish of a continuous casting plant from a bottompour ladle 10 which comprises an outer metal casing 11 and a refractorylining 13. A nozzle assembly 12 is mounted in the ladle 10 and comprisesa refractory nozzle tube 14 supported within refractory blocks, 16, 18and in a refractory outer nozzle member 19 mounted in a metal mountingplate 20 secured to the outer metal casing 11 of the ladle 10 by bolts326 (FIG. 8). A stationary refractory orifice plate 22 is securedgenerally below the mounting plate 20 and comprises an orifice 24 inalignment with the nozzle tube 14.

The sliding gate valve assembly also comprises a framework 26 removablysecured to the mounting plate 20 by a toggle mechanism 334 as describedin more detail in said Shapland et al. Application; a sliding gatecarrier 28 is mounted for horizontal sliding movement in the framework26. The horizontal sliding movement of the carrier 28 is effected by ahydraulic cylinder and piston assembly 29 mounted in a bracket 30 of theframework 26. A refractory sliding gate 32 is supported in the carrier28 and comprises a nozzle tube 34 extending downwardly from the regionof the sta tionary plate 22. The nozzle tube 34 is supported in upperand lower refractory ring members 36, 38. A lower surface of thestationary plate 22 provides an upstream seating for the sliding gate32.

It will be realised that the sliding gate 32 is movable between a closedposition as shown in FIG. 1 in which the tube 34 is not aligned with theorifice 24, and an open position (not shown) in which the tube 34 isaligned with the orifice 24 and molten steel is free to flow from theladle 20 into the ingot mould or tundish through the tube 14, theorifice 24 and the tube 34.

The sliding gate 32 is urged against the stationary plate 22 intosealing engagement therewith by a plurality of spring devices 42 spacedaround the tube 34; there are for example between 8 and 18 springdevices 42, 12 being shown in FIG. 9. Each spring device 42 acts betweenthe carrier 28 and the sliding gate 32, being received in a bore 62(FIG. 2) in the carrier 28. The spring devices 42 are arranged in apredetermined pattern around the nozzle tube 34 as shown in FIG. 9.

The piston and cylinder assembly 29 comprises a hydraulic cylinder 316to which hydraulic fluid is supplied via hydraulic lines 362. A piston363 is mounted in the cylinder 316 and is secured on a hollow ramrod365. The ramrod 365 extends through a ramshield 364 to be secured to thegate carrier 28, the ramshield 364 being secured in the bracket 30. Anair hose 361 is provided to continuously flow air through the hollowramrod 365 not only for cooling the cylinder 316 but also the carrier 28and the spring devices 42. The carrier 28 has for this purpose aplurality of connected air chambers 375 interiorly thereof, and the airhose 361 coupled to the hollow ramrod 317 delivers a constant stream ofair to the air chambers 375 thereby cooling the carrier 28 4 and springdevices 42. The air may be dry or humid or alternatively carbon dioxidemay be used.

The stationary plate 22 fits within a recess in the mounting plate 20(FIGS. 1 and 10) and also the stationary plate 22 contains a centralannular groove proportioned to receive an annular ring 308 of the outernozzle member 19.

The plate 22 comprises two straight parallel sides joined bysemi-circular end portions and comprises a refractory body 309 encasedin a thin-walled steel casing 310. The refractory body 309 is secured inthe casing 310 by means of a heat settable cement. A circular opening310a (FIG. 1) is provided in the metal casing 310 adjacent the annularring 308 to provide for a ceramic joint, and it will be realised thatthe casing 310 leaves the lower surface 40 exposed. A mastic refractoryfiller (for example as described in Cudby Application Ser. No. 380,808of common ownership) is desirably inserted between the metal casing 310and the plate 22 to accommodate irregularities. Thus the refractory bodyof the stationary plate 22 is encased so that in event of cracking, thesame will be contained in position.

The sliding gate 32 similarly comprises a refractory body provided bythe tube 34 and ring members 36, 38; this refractory body comprises anupper portion having straight parallel sides and semi-circular endportions corresponding to the stationary plate 22 and a lower circularcylindrical portion. Again, the refractory body is encased in athin-walled steel casing 370, while leaving exposed an upper surface ofthe member 36 and a lower surface of the member 38 and nozzle tube 34.Again, the refractory body is secured in the casing 370 by a heatsettable cement and the mastic refractory filler may be used.

The nozzle tube 34 of the sliding gate 32 consists of a highly erosionresistant refractory material and the lower ring member 38 surroundingthe nozzle tube 34 is of low conductivity refractory material. The upperring member 36 is of an abrasion resistant refractory materialcomparable to that of which the stationary plate 22 is formed.

The highly erosion resistant refractory material for example has a highcontent of alumina, normally in the range of to by weight. This materialhas a high density and is high temperature fired. The faces of suchmaterial often must be ground to exact shape. On the other hand thebackup refractory, such as employed in the blocks 16, 18, and the ringmember 38 may have for example a low alumina porous structure which maybe castable; alternatively a fired material may be used. Also usable asto an altemaitve is a fused silica castable material.

The slidably engaging surfaces of the member 36 and the stationaryorifice plate 22 are ground and polished to provide required sealingcharacteristics.

It will be noted from FIG. 10 that the orifice plate 22 is symmetricalin plan view about each of the two axes at right angles; and the slidinggate 32 is similarly symmetrical; this enables reversal of the orificeplate 22 and the sliding gate 32 to even the effects of erosion.

Each spring device 42 (FIG. 2) is self-contained and comprises opposedupper and lower pad members 44, 46 respectively. The upper pad member 44is in engagement with the metal casing 370 of the sliding gate member 38and the lower pad member 46 which is annular is remote from the gatemember 38 being in engagement with a horizontal machined annularshoulder 48 provided in the appropriate bore 62 of the sliding gatecarrier 28. The pad member 44 is fixed to a vertical core member 50 by ascrew 52 which is screwed into a threaded bore 54 in the core member 50;altematively the pad member 44 may be integral with the core member 50.The annular pad member 46 is mounted freely on the core member 50 whichextends downwardly through the annular pad member 46 into a recess 56which extends downwardly from the shoulder 48. A circlip 58 is fittedinto an annular groove 60 in the core 50 to retain the annular padmember 46 prior to fitting of the spring device 42 into the carrier 28.It will be realised that the pad members 44, 46 are mounted in the coremember 50 for relative movement of the pad members 44, 46 in thedirections longitudinal of the core member 50.

A resilient O-ring 64 fitted into an annular groove 66 in the member 46serves to locate the device 42 firmly in the bore 62.

A sleeve 68 is slidably mounted on the core member 50 between the padmembers 44, 46. An upper end portion of the sleeve 68 is provided withan annular shoulder 70, and the lower end portion of the sleeve 68 isprovided with an annular shoulder 72. The upper end portion of thesleeve 68 is received in a recess 68a in the pad member 44. A firstspring assembly comprising six conical disc springs 74 are mountedaround the sleeve 68 seated against the annular shoulder 70 and inengagement with the pad member 44, and similarly a second springassembly comprising two conical disc springs 76 are mounted also aroundthe sleeve 68 but seated against the shoulder 72 and in engagement withthe pad member 46. The disc springs 74 act in series and the discsprings 76 act in parallel.

An example of a conical disc spring (sometimes known as a Bellevillewasher) is shown in FIG. 6; the disc spring shown in FIG. 6 comprises adisc of suitable metal with a central hole 80 to which a frusto-conicalside wall 82 converges. The outer periphery 84 of the disc is circularcylindrical, being coaxial with the hole 80. If a plurality of such discsprings are mounted coaxially together in series, i.e. with adjacentdiscs inverted with respect to each other, the load deflectioncharacteristic of the series is the same as for a single disc. If on theother hand, a plurality of disc springs are mounted coaxially togetherin parallel, i.e. with all discs converging in the same direction, theload required to give a particular deflection is multiplied by thenumber of disc springs in parallel. Thus, then, assembly of springs 76in parallel is more preferred than the assembly of springs 74 in series.

In normal operation of the spring device 42, the springs 76 in parallelhave a higher load deflection characteristic than the spring series 74.The sleeve 68 extends longitudinally of the core member 50 towards thepad member 46 to leave a small gap 800 between a lower end face of thesleeve 68 and the pad member 46. Thus, the springs 74 are resilientlyoperative and act between the sleeve 68 and the pad member 44 to urgethe pad member 44 upwardly against the sliding gate member 38; again,there is a small gap 82a left between an upper end face of the sleeve 68and the pad member 44. The actual width of the gap 82a varies inaccordance with the accuracy of manufacture of the sliding gate andassociated parts, but does not exceed about ten thousandths of an inch.

Disc springs are generally less likely to fail under heat and otherstresses than coil springs, but in the event of failure of the springseries 74, the pad member 44 moves downwardly to close the gap 82a andit will be realised that its downward movement is severely restricted,being defined by the width of the gap 82a, and that movement of thesliding gate 32 away from the stationary orifice plate 22 iscorrespondingly severely restricted.

In the event that excessive manufacturing tolerances cause closure ofthe gap 82a against action of the spring series 74 (without failurethereof) rendering the springs 74 inoperative, the springs 76 becomeresiliently operative to act with twice the load deilectioncharacteristic of the series 74 to maintain resilient urging of thesliding gate against the stationary plate 22.

It is rather unlikely that the springs 76 will be subject to failure,but in that event the resultant downward movement of the sleeve 68 isdefined by the width of the gap a which is for example no more thantwenty thousandths of an inch. Thus, in the event of failure of thespring series 74 and the springs 76, the total downward movement wouldbe limited to thirty thousandths of an inch. With movement of thesliding gate 32 away from the stationary orifice plate 22 of only ten orat the most thirty thousandths of an inch, the risk of large scaleleakage of molten metal is minimised.

It will be realised that in any case failure of the series 74 will notnecessarily always involve failure of the entire complement of thesprings 74; it is perfectly possible for one spring to fail and theothers to remain effective; similarly in the case of the springs 76.

In a modification the springs 76 are omitted, in which case the sleeve68 is at all times in engagement with the pad member 46; in this casefilure of the spring series 74 is still catered for, but excessivemanufacturing tolerances are not so well covered.

In another modification thin washers are located between the pad member46 and the springs 76 to limit further the possible downward movement ofthe sleeve 68 in the event of failure of the springs 76.

The first modified spring device (FIG. 3) resembles that shown in FIG. 2in many respects and is described in so far as it differs therefrom. Thedevice shown in FIG. 3 comprises upper and lower pad members 144, 146and a core member 150. A sleeve 168 is mounted on the core member 150. Asingle disc spring acts between and is in engagement with the sleeve 168and the pad member 146, and fulfils the same function as the springs 76of FIG. 2. A coil spring 192 surrounds the sleeve 168 and acts betweenand is in engagement with the disc spring 190 and the pad 144,fulfilling the same function as the spring series 74 of FIG. 2.

The second modified spring device (FIG. 4) again resembles that shown inFIG. 2 in many respects and is described in so far as it differstherefrom. The device shown in FIG. 4 comprises pad members 244, 246,and a core member 250. A coil spring 294 acts between and is inengagement with the pad members 244, 246. This coil spring has closelyspaced loops 296 and in the event of failure of the spring, downwardmovement of the pad 244 is severely restricted by the spacing of theloops.

The third modified device (FIG. 5) resembles that shown in FIG. 4 inmany respects and is described in so far as it differs therefrom. Thethird modified device comprises upper and lower pad members 444, 446, acore member 450 and a coil spring 494 as in FIG. 4, but the coil spring494 has normal loop spacing. The coil spring 494 is surrounded by arelatively powerful band spring 500 which comprises a spiral band; thisis located between the pad members 444, 446 so that it comes intooperation only in the event of abnormal downward movement of the upperpad member, there normally being a gap between the band spring and thepad member 444. In a sliding gate valve assembly incorporating such bandsprings, it may be necessary only to use the devices with band springsin some of the positions around the nozzle tube of the sliding gate.prior art spring devices being used in the remaining positions; e.g.three or four devices incorporating band springs may be used out of atotal of eight to 16.

The fourth modified spring device (FIG. 7) again resembles that shown inFIG. 4 in many respects and is described in so far as it differstherefrom. The fourth modified device comprised upper and lower padmembers 544, 546, a core member 550 and a coil spring 594, but again thecoil spring 594 has normal loop spacing. However, the core member 550extends in a direction away from the sliding gate member 32 into therecess 56 in the carrier 28 towards stop means provided by a base wall56a of the recess 56 so that a lower end face of the core member 550 isclosely adjacent the base wall 56a of the recess 56; downward movementof the core member 550 and thus of the pad member 544 is severelyrestricted by the width of the gap between the lower end face of thecore member 550 and the base wall 56a; the width of this gap is forexample no more than twenty five or thirty thousandths of an inch.

The steel used in the casings for the refractory bodies is very ductile,for example a hot rolled pickled and oiled grade for drawing; in somecases deep drawing or extra deep drawing quality may be specified.

Suitable spring manterials for disc coil or band springs operating athigh temperatures include the following according to the maximumoperating temperature; 18/8 Stainless Steel; nickel/chromium alloys; andtitanium/vanadium alloys.

For example, 18/8 Stainless Steel can be used up to about 450C; andnickel/chromium alloys up to about 600C.

Disc springs are available for example from Messrs. S.A.M. EquipmentLimited of Sheffield, England, in sizes ranging from 1 inch to 24 inchesin diameter and thicknesses ranging from 26 SWG to more than /8 inch.

Disc springs are produced with various load deflection characteristicswhich are not necessarily rectilinear but may be for exampleprogressive, regressive or inverted; this may be of particularimportance in regard to the springs 76.

It will be realised that spring devices embodying the invention and themetal encased refractory parts which have been described hereinbeforemay be incorporated in sliding gate valve assemblies for tundishes orother metal holding vessels or furnaces, as well as for ladles in thecontinuous casting of steel.

Again, it will be realised that spring devices embodying the inventionare readily adapted to sliding gate valve assemblies as described in theaforementioned J. T. Shapland and Lyman patents.

Although the above description has been given with reference to a bottompour vessel it will be realised that sliding gate assemblies embodyingthe invention may also be incorporated in for example side pour vessels.

In a modification the sliding movement of the carrier 28 is effected bya piston and cylinder device mounted on a side wall of the ladle 10 asdescribed in US. patent application Ser. No. 300,957 of J. J. Klaus andE. P.

8 Shapland with particular but not exclusive reference to FIG. 7thereof.

In another modification the refractory ring member 36 of the orificeplate 22 is of identical shape and dimensions to the refractory body 309of the sliding gate 32, and in this case an upper end portion of thenozzle tube 34 terminates just below the ring member 36 rather thanextending through the ring member 36.

I claim:

1. In a sliding gate valve assembly for controlling flow of moltenmetal, which assembly comprises a sliding gate member, a seating forsaid gate member, and resilient devices urging said gate member intosealing engagement with said seating, the improvement in which each ofsaid devices comprises:

a core member;

two spaced-apart pad members mounted on said core member for relativemovement in directions longitudinal of said core member;

a sleeve member slidably mounted on said core member intermediate saidpad members and extending longitudinally of said core member;

spring means around said core member acting to urge said pad membersapart; and

means including said sleeve member acting to restrict severely relativemovement of said pad members toward each other to restrictcorrespondingly movement of said gate member away from said seating inthe event of failure of said spring means.

2. The improvement according to claim 1, wherein a small gap is normallyleft between each pad member and an adjacent end face of the sleevemember, said gaps defining said restricted relative movement of the padmembers.

3. The improvement according to claim 2, wherein end portions of thesleeve member are each provided with an annular shoulder, and the springmeans comprises a first spring assembly seated against the annularshoulder and in engagement with one pad member and a second springassembly seated against the other annular shoulder and in engagementwith the other pad member, the second spring assembly being morepowerful than the first spring assembly.

4. The improvement according to claim 3, wherein each spring assemblycomprises a plurality of disc springs.

5. The improvement according to claim 3, wherein the first springassembly comprises a plurality of disc springs acting in series, and thesecond spring assembly comprises a plurality of disc springs acting inparallel.

6. The improvement according to claim I, wherein the spring meanscomprises a disc spring acting between and in engagement with the sleevemember and one of the pad members.

7. The improvement according to claim 6, wherein the spring means alsocomprises a coil spring acting between and in engagement with the discspring and the other pad member.

8. A sliding gate valve assembly according to claim 1, wherein thesliding gate member comprises a refractory body and a thin-walled metalcasing encasing said refractory body.

9. A sliding gate valve assembly according to claim 1, comprising astationary orifice plate providing the seating for the sliding gatemember and comprising a refractory body and a thin-walled metal casingencasing said refractory body.

10 of the orifice plate and sliding gate comprises in plan view twostraight sides, two semi-circular end portions joining the sides, and acentral circular orifice, and is symmetrical about each of two axes atright angles.

1. In a sliding gate valve assembly for controlling flow of moltenmetal, which assembly comprises a sliding gate member, a seating forsaid gate member, and resilient devices urging said gate member intosealing engagement with said seating, the improvement in which each ofsaid devices comprises: a core member; two spaced-apart pad membersmounted on said core member for relative movement in directionslongitudinal of said core member; a sleeve member slidably mounted onsaid core member intermediate said pad members and extendinglongitudinally of said core member; spring means around said core memberacting to urge said pad members apart; and means including said sleevemember acting to restrict severely relative movement of said pad memberstoward each other to restrict correspondingly movement of said gatemember away from said seating in the event of failure of said springmeans.
 2. The improvement according to claim 1, wherein a small gap isnormally left between each pad member and an adjacent end face of thesleeve member, said gaps defining said restricted relative movement ofthe pad members.
 3. The improvement according to claim 2, wherein endportions of the sleeve member are each provided with an annularshoulder, and the spring means comprises a first spring assembly seatedagainst the annular shoulder and in engagement with one pad member and asecond spring assembly seated against the other annular shoulder and inengagement with the other pad member, the second spring assembly beingmore powerful than the first spring assembly.
 4. The improvementaccording to claim 3, wherein each spring assembly comprises a pluralityof disc springs.
 5. The improvement according to claim 3, wherein thefirst spring assembly comprises a plurality of disc springs acting inseries, and the second spring assembly comprises a plUrality of discsprings acting in parallel.
 6. The improvement according to claim 1,wherein the spring means comprises a disc spring acting between and inengagement with the sleeve member and one of the pad members.
 7. Theimprovement according to claim 6, wherein the spring means alsocomprises a coil spring acting between and in engagement with the discspring and the other pad member.
 8. A sliding gate valve assemblyaccording to claim 1, wherein the sliding gate member comprises arefractory body and a thin-walled metal casing encasing said refractorybody.
 9. A sliding gate valve assembly according to claim 1, comprisinga stationary orifice plate providing the seating for the sliding gatemember and comprising a refractory body and a thin-walled metal casingencasing said refractory body.
 10. An assembly according to claim 9,wherein the sliding gate member also comprises a refractory body and athin-walled metal casing encasing the refractory body.
 11. An assemblyaccording to claim 10, wherein each of the orifice plate and slidinggate comprises in plan view two straight sides, two semi-circular endportions joining the sides, and a central circular orifice, and issymmetrical about each of two axes at right angles.